Turnover of the chemosensory cells of the gustatory and olfactory system necessitates substantial neuronal growth and remodelling of synaptic connections in the peripheral and central nervous systems. Experiments within this project are designed to test the degree of neuronal growth and plasticity in these systems through the use of immunocytochemical probes which are directed against neuronal growth-related antigens. These experiments will examine primary chemosensory nerves and the receptor cells of the taste buds for evidence of immunoreactivity to antibodies directed against the neuronal membrane proteins 5B4 and GAP- 43, both of which are present in high levels in growing neurons but are reduced in synaptically stable neurons. Taste bud cells themselves will be tested for the presence of GAP-43 since some taste cells express 5B4 immunoreactivity. Tritiated thymidine techniques will be utilized to correlate the presence of these immunoreactivities with relative age of the taste cells. Primary gustatory nerve terminals within the CNS also will be tested for immunoreactivity to these growth-related markers. In addition, the ultrastructure of primary gustatory terminals within the CNS will be examined in a continuation of our studies attempting to relate terminal morphology to chemospecificity. Finally, the olfactory system will be examined for 5B4 and GAP-43 immunoreactivities since olfactory neurons continue to be generated and grow into adulthood. Biochemical maturation of the receptors will be studied by means of immunoreactivity to olfactory marker protein, and the growth-related neural antigens. In addition, collaborative studies will continue in terms of determination of the taste bud neurotransmitter, identification of neuropeptides in human biopsy material, and delineation of nerve fibers within taste buds.